Patent GB-210733-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1923-09-04
Abstract: 210,733. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Ray, A. J.). Feb. 2, 1923, [Convention date]. Addition to 196,245. Automatic exchange systems.-In a system in which, upon the initiation of a call at a satellite exchange, an idle trunk to the main exchange is selected and the first digit or digits of the wanted number are repeated over the trunk to operate main-exchange switches simultaneously with the operation of a local discriminating switch as described in the parent Specification, trunks lead directly from the satellite to adjacent satellites which may belong to different main exchanges, and if the first digits dialled denote one of these adjacent exchanges, the main exchange connection is released and the local switch hunts automatically for an idle trunk to the exchange desired. Special provision is made to prevent the local switch from switching over and releasing the main-exchange connection in response to a series of digits which is made up of one or more digits from two different local or adjacent satellite designations but which itself represents a connection which can only be completed through the main exchange. The system shown represents part of a 100,000-line system comprising 10,000-line main exchanges each distinguished by a particular first digit and a number of 100-line satellite exchanges each represented by a particular combination of the first three digits. When a subscriber A, Fig. 1, in satellite 914, initiates a call, he is connected in known manner to an idle selector-repeater D, Fig. 2, of Strowger type, associated with which is a line switch C<3> which selects an idle trunk 138, 139, leading to the main exchange, Fig. 3. The two terminals in the lower bank and the lower terminals in the upper bank, Fig. 4, of the switch D are multipled in the usual manner, over the fourth level to trunks 259, 260 leading to local connectors, and over the second and third levels to trunks 287, 288; 275, 276 leading to adjacent satellite exchanges 232, 763, respectively. The upper terminals of the upper bank, Fig. 4, are not multipled, but are wired to relays &c. as shown, these connections causing circuit changes which, whilst effecting the release of the main-exchange connection and the selection of an idle trunk by the switch D in the case of a number, the first three digits of which are 914, 763 or 232, prevent such operations in response to a digit-combination 913, 764, &c. If a call is not for the local or an adjacent satellite, all further movement of the switch D is prevented as soon as this fact is established, which may be after the first, second or third digit, and the switch acts thereafter only as a repeater for further impulses. The selectorrepeater D is similar to that shown in Specification 174,332, but is modified as regards dialling tone, in that this tone is only supplied from the switch D if all the main-exchange trunks are busy, but in other cases is transmitted back from the main exchange. Initiation of call and selection of idle trunk to main exchange. The calling subscriber A having been connected in known manner to an idle switch D, the operation of line relay 35 closes a bridge 66, 38, 44, 53, 93 across conductors 101, 105 to energize relay 119, whilst. the release relay 36 grounds lead 102. Relay 119 connects the test wiper 132 to the stepping magnet 117 and the switch C<3> is stepped round until an idle trunk is reached, when switching relay 118 operates and closes a parallel circuit through a relay 120 which marks the selected trunk busy, relav 119 remaining locked up over contacts 124, 127. As soon as relay 118 operates, the line relav 151 of the first main-exchange selector E energizes, and dialling tone is transmitted from a machine T<1>. Local call to subscriber No. 91467 in same satellite. The first set of impulses is repeated by line relay 35, at, armature 93 to the main exchange, and at armature 57 to the vertical magnet 47 to raise the switch D to its ninth level. Shaftsprings 97, 98 are operated when the switch is raised to its second, seventh or ninth level, corresponding to the first digits of the satellites accessible over the switch D, so that, in this case, the second set of impulses is repeated over contacts 69, 74, 97 to the rotary magnet 46. The wiper 251 is thus brought on to the first terminal 266 in the ninth level, and, when relay 37 relapses at the end of the digit, relay 255 energizes over the circuit 266, 95, 65 in series with marginal relay 43. Relay 255 locks up over its lower winding to the grounded lead 32, removes ground from the first terminal 269 in the fourth level so as to permit hunting over this level after the third digit, and short-circuits its upper winding, thereby permitting relay 43 to energize. Relay 43 closes a circuit 95, 87, 86, 70, 79 for the release magnet 48 which energizes and closes a locking circuit for itself and for relay 43 until the switch is completely restored to normal, when the deenergization of relay 39 opens contacts 70. Relay 42 now energizes over its lower winding in series with the release magnet and locks itself over its upper winding to the grounded conductor 32, whilst the release magnet de-energizes. The third set of impulses is repeated as before to operate the vertical magnet 47, whilst the stepping relay 41 energizes over circuit 80, 85, 72, 50, 64, 62 and locks up over the interrupter-contacts of the rotary magnet 46. At the end of the digit, the relapse of relay 37 completes circuit 75, 64, 62 for the rotary magnet and the wipers of the switch are thus automatically rotated in the usual manner over the fourth level until an idle local trunk 259, 260 is reached, when the operation of switching relay 45 connects conductors 31, 33 directly to the trunk 259, 260, and the remaining impulses are transmitted over this trunk to a local connector which completes the connection in known manner. Release of main-exchange connection; means for dealing with defective trunks. The breaking of the bridge across conductors 101, 105 releases the main exchange switches, whilst the release of relay 36 causes the de-energization of relays 118, 119, 120, the two latter being slow in releasing so that the rotary magnet 117 energizes over contacts 127, 124, 141 to advance the wipers one step. Thus, should the trunk to which a calling subscriber first gets access be defective, he will, upon hanging up and calling a second time, be connected to a different trunk. Call to subscriber No. 76367 in adjacent satellite exchange 763. In this case, the call proceeds in a similar manner to that alreadv described for a local call, a relay 270 being locked up and the switch D released after the second digit, whilst after the third digit the wipers automatically rotate over the third level to select an idle trunk 275, 276 to the adjacent satellite. Call to subscriber No. 91367, reached only through the main exchange. In response to the first two digits, relays 255, 42 are locked and the switch D released as before. In response to the third digit, the switch is raised to the third level and rotated one step so that wiper 251 engages terminal 274 which is grounded over contact 273. Before the rotary magnet de-energizes due to the de-energization of the stepping relay, relay 43 energizes over contacts 65, 251, 273 and opens the circuit of the stepping magnet to prevent further rotation, so that the switch D only operates thereafter as a repeater, and the connection is completed over main-exchange switches E, E<1>, E<2>, H. Call to subscriber No. 95567 in main exchange. The switch D operates as before in response to the first digit, but wiper 251 is rotated by the second digit on to a terminal 263 which is grounded over a resistance R. Upon the relapse of relay 37, relays 43, 42 energize as before, but the release magnet is unable to energize in series with the resistance R and the switch remains in its operated position and acts as a repeater for further impulses. Call to subscriber No. 84567 in distant exchange. In this case, in which it is apparent after the first digit that the call cannot be completed over switch D, springs 97, 98 are not operated so that the second digit is not repeated to the rotary magnet, but is repeated with the remaining digits over the trunk 138, 139, and the connection is completed through the main exchange. Call to adjacent satellite 232 having first and third digits the same. In order that, after the second digit, the terminal 278 in the second level may be connected to a relay 280 similar to relay 255, whilst after the third digit, all the upper terminals in the second level may be disconnected so that hunting is permitted, an additional relay 281 is provided which is operated by relay 280 and disconnects ground from contact 279, whilst relay 280 has a low-resistance lower winding which permits relay 43 to energize. Thus, when relay 280 de-energizes during the release of the switch, it is unable to energize again. Call to line having a third digit 9. Since terminal 266 is normally grounded over the highresistance upper winding of relay 255, whilst, in the case of a call to a line of which the first two digits correspond to a locally-reached satellite whilst the third does not, it is necessary for the relay 43 to energize upon the first rotary step after the third digit, relays 270, 281 are provided with contacts which short-circuit relay 255 by directly grounding terminal 266. Dialling tone. This is normally supplied from a machine T' over the lower winding of line relay 151 of first selector E, Fig. 3, but if no idle trunk to the main exchange is available, relay 144 is operated to prevent the operation of relay 119 so that dialling tone is transmitted from machine T at the switch D over contacts 71, 98, 128, 122, 66, 54. Busy tone. Since the call may be one which can be completed locally, the fact that all mainexchange trunks are busy i